class: center, middle, inverse, title-slide # Lecture 7 ## Paired Samples ### Psych 10 C ### University of California, Irvine ### 04/13/2022 --- ## Paired samples - Until now we have been working with an experimental design known as **between subjects** design. -- - This means that each participant in our sample can only be included in one group at a time. -- - For example, in the smokers data, participant can be either on the smokers group or on the non-smokers group but they can't be in two. -- - We call this a **between subjects** design because the data of one group of participants is compared with data from a different group of participants -- - However, we could have a design where each participant can respond in our two groups. --- # Example - **Problem:** We are at the end of the semester at a university and we want to know if our students have improved their grades. -- - There is variability in grades but we wold like to make a generalization, and say that either they improved during the semester or that they didn't (as a group). -- - To solve this problem we can use the students' scores on the midterm and their scores on the final. -- - However, notice that the observations between the groups will be correlated. This is a problem for our approach, as we stated in our model that the observations that we had where independent! -- - The correlation in our observations comes from the fact that we are measuring the same participant twice. The student 1 miterm and final score will have some degree of correlation because they come from the same person. -- - In order to avoid the problem of correlations between our two observations we need to get reed of the "redundant" information. -- - A simple way to get rid of it is by just taking the difference between the two socres.